The overall objective is to conduct research on the development of an intravascular membrane lung with the goal of providing sufficient oxygen and carbon dioxide exchange capability to support an adult human. The proposed device has short (<1 cm) microporous hollow fibers attached radially to a concentric pulmonary artery catheter. The central catheter will contain two lumens for gas flow. One will serve as the gas inlet for delivering 100% oxygen to the fibers while the other will serve as a gas outlet for flushing away carbon dioxide from the fibers. The distal end of each hollow fiber will be sealed and float free in the blood stream. Initial studies will focus on gas transfer in single fibers and simple fiber arrays to determine how gas transfer is affected by gas supply pressure, blood flow, fiber size, fiber orientation, interactions between fibers, and liquid chemistry. More advanced prototypes with increasing numbers of fibers will be built and tested. Studies will include the effect of secondary flow on gas exchange, and assessment of damage to formed elements of the blood. Upon development of a suitable final prototype, in vivo studies will be conducted to demonstrate that the device can support gas exchange of an anesthetized sheep. Additional studies in sheep will be undertaken to ensure that the device does not obstruct venous return, does not cause right heart failure, and can be easily inserted and removed.